The invention concerns a hoisting device, especially a cable or chain block, with a gearing having at least one shaft and with a load measuring mechanism.
Hoisting devices like cable or chain blocks have a predetermined lifetime, which depends on the load stress and the load frequency distribution. Furthermore, an economical use of hoisting devices requires a high capacity utilization. In order to determine the remaining lifetime each year, one therefore requires, at a minimum, the hours of operation and their load frequency distribution as data.
Formerly, the data needed to determine the hours of operation and the load frequency distribution were gathered manually or estimated. However, this is time-consuming and inaccurate. Methods and devices were therefore developed to automatically count the hours of operation, so-called operating hour counters. Corresponding methods and devices for monitoring of hoisting devices are known, for example, from DE 195 14 050 C2, DE 196 17 105 C2, DE 199 23 824 C2, DE 199 56 265 A1 and DE 40 38 981 A1.
The monitoring data are automatically gathered by means of these methods and with these devices, saved if so required, and put out via displays, wherein both the devices and the displays are usually arranged in the hoisting device. For this, it is known how to perform either a manual, optical reading of the displays or how to electronically read out the data by means of an interface and corresponding reading device.
Besides the hours of operation, the load frequency distributions are also kept track of. For this, one needs to determine the hoisting load.
But the hoisting load measurement is also useful to the safety, since the hoisting devices are designed for a maximum load, which must not be exceeded.
To avoid such overloading of the hoisting device, it is known, for example from DE 34 42 868 A1, how to employ end switches which shut off the hoisting device after exceeding a predetermined spring force corresponding to the maximum load. Although this ensures the safety of the hoisting device in operation, no direct measurement of the actual hoisting load is possible.
Therefore, for actual measurement of the hoisting load, one often uses load measuring mechanisms with measuring elements such as strain gauge strips, which enable a determination of the actual load in terms of the strain in the measurement strips. Furthermore, these are usually also combined with end switches.
The usual devices, however, have a number of drawbacks. They are costly and cumbersome. The strain gauge strips are usually not loaded directly by the full hoisting load, but instead are mechanically reduced, e.g., via suitable levers. But this leads to an increased physical size, especially the structural height. Moreover, only the force acting on the cable strand (or chain) is determined, but this is dependent on the reeving of the cable, so that this has to be factored into the absolute determination of the hoisting load. Also, no measurement without reeving is possible in these devices, since the measurement is done in the load string. On the whole, therefore, the usual devices involve a relatively elaborate evaluation of the signals and circumstances of the load measurement, requiring special electronics for the evaluation, in order to achieve the desired accuracy.
From German Utility Model DE 203 00 942 U1 is known a force transducer for the measuring of axle forces that essentially act transversely on an axle. Such a force transducer can be used, for example, to measure the forces acting on a cable drum, in order to prevent an overloading of the cable drum or the attached device. The force transducer essentially has a lengthwise extending axial body on a first segment for mounting of the cable drum, designated as the force entry zone. This first force entry segment is followed by two force measuring zones on either side, which have a smaller diameter than the force entry zone, as well as the bearing zones adjoining the force measuring zones. In the region of the bearing zones, the axle is mounted in appropriately configured cheeks. Within the force measuring zones there are blind boreholes oriented transversely to the lengthwise dimension of the axle, in which strain gauge strips are arranged. These blind boreholes are hermetically sealed at the outside with a cover, so that the force measuring system is protected against environmental influences. For reasons of redundancy, a blind borehole with strain gauge strips is arranged in each of the opposite force measuring zones in relation to the cable drum. The strain gauge strips can measure stresses, elongations, and shear forces of the material of the axle body in the region of the force measuring zone. The resulting measurement signals can then provide information as to the loading of the cable drum.
Moreover, from German Patent DE 195 12 103 C2 there is known a cable winch with an operating data gathering system. Besides a determination of the number of revolutions and direction of turning, the loading of the cable winch is also measured by torque sensors. This cable winch is essentially characterized by a cuplike pillow block at one side, serving to accommodate a hydraulic motor, and projecting into a cable drum of the winch. The output shaft of the hydraulic motor acts via a gearing on the cable drum of the winch. Torque sensors in the form of strain gauge strips are arranged at the outer circumference of the stationary cuplike pillow block, by which one can measure the loading of the cable winch as a function of the deformation of the pillow block.
Furthermore, from German Patent DE 35 17 849 there is known a torque sensor for a steering shaft or a transmission shaft of a motor vehicle. The shaft consists of a ferromagnetic material or a nonferromagnetic material that is covered with a film of ferromagnetic material. The torque sensor measures without contact the torque exerted on the shaft by sensing the magnetic permeability of the shaft. For this, the torque sensor has an excitation winding unit with two excitation coils and a sensor winding unit with two sensor coils. Since the magnetic fluxes of the excitation coils operated by alternating current pass through the shaft, the electrical signals generated in the sensor coils are dependent on the magnetic permeability of the shaft and, thus, on the torque exerted on the shaft.